The following description is provided solely as background and without admission of “prior art” status of any of the structures and processes disclosed therein within the legal meaning of that term.
Conventional ball grid array (BGA) packages 600 are based on a plastic packaging substrate 601 as illustrated in FIG. 6. Heat dissipation occurs mainly by conduction from the integrated circuit die 602 through the packaging substrate 601 and the solder balls 603 to the printed circuit board (PCB) 604. The plastic packaging substrate 601 has a very low thermal conductivity (0.2 Watts per meter per degree Celsius or W/m/° C.) and is therefore generally poor in both heat conduction and heat spreading (arrows indicate heat conduction).
BGA and equivalent land grid array (LGA) packages are often compared to thermally enhanced lead frame packages such as the exposed pad (epad) thin quad flat package (TQFP) 700 illustrated in FIGS. 7A and 7B, in which the integrated circuit die 701 is attached to the die pad (or paddle) 702, which is in turn directly soldered to the PCB 703 by solder regions 704. The heat conduction path includes the copper lead frame die pad 702, which has a high thermal conductivity such as copper (400 W/m/° C.) contributing to the low thermal resistance for the package. It would be desirable for a BGA/LGA package to have equivalent thermal performance to epad TQFP so that BGA/LGA packaging may be employed to accommodate the same electrical and thermal performance requirements.
To achieve such thermal enhancement, a copper heat slug/copper heat spreader BGA (C2BGA) package 800 has been proposed, as illustrated in FIG. 8. C2BGA package 800 employs a bi-layer substrate 801 including a non-conductive (e.g., plastic, fiberglass, or epoxy) portion 802 with an opening therethrough and covered by a copper heat spreading layer 803. A copper heat slug 804 having a bottom with a solderable finish is attached to the substrate 801 by an adhesive 805, preferably thermally conductive, such as an electrically conductive glue or solder. The integrated circuit die 806 is directly attached to the heat slug 804, which in turn is soldered to the PCB 807. Heat is dissipated outward toward the solder balls by the heat spreader layer 803 and directly conducted to the PCB 807 through the high thermal conductivity heat sink 804 and the solder balls.
C2BGA package 800 has a thermal performance equivalent to that of an epad TQFP package. However, since the C2BGA package 800 is not flat due to the attached slug, specialized wire bonding and molding tooling are required for packaging. In addition, there are challenges in the slug attachment to the substrate, including making a void free attachment with a consistent bond line and tight lateral (x-y) placement tolerance.
There is, therefore, a need in the art for an improved thermal performance ball grid array package that allows the same tooling to be employed for package assembly as conventional ball grid array packages, with consistent placement of the heat slug/spreader.